The present invention relates, in general, to microwave systems and, more particularly, to microwave system integration involving devices that are disposed on two or more dies and are electrically coupled.
There is a continuing trend to integrate the various components of a microwave system into a single package. An example of this integration is exhibited by conventional monolithic microwave integrated circuits (MMICs). However, one problem affecting the use of an MMIC is a significant disparity in the fabrication requirements for different types of devices formed on the MMIC. For example, some types of devices on the MMIC only require a low number of processing steps to form, or they are easy to manufacture due to their relatively large geometries. Such devices usually have a high manufacturing yield. One example of such a device is a spiral inductor. In contrast, other types of devices on the MMIC require a relatively large number of processing steps to form or have relatively small geometries, resulting in lower manufacturing yields for these devices. An example of this type of device is a power field effect transistor (FET) having a short gate length.
As a result of the above disparity in manufacturing standards for different devices on an MMIC, the overall yield for the MMIC is disproportionately reduced by the presence of only a small number of low-yielding devices. This is so even though the low-yielding devices typically account for only a small portion of the total layout area of the MMIC. Thus, an MMIC containing predominantly functional devices often must be scrapped solely because one or a few low-yielding types of devices, which occupy only a small portion of the MMIC's total layout area, are found to be non-functional.
Another weakness of prior MMIC integration approaches is their reliance on a gallium arsenide substrate. Gallium arsenide is more difficult to handle and more expensive to process than silicon. Although gallium arsenide has been used widely in the past due to its high resistivity, it would be desirable to form MMIC devices on a silicon substrate due to silicon's low cost and the ability to use well-established silicon processing techniques.
Accordingly, there is a need for a structure and method for integrating microwave devices that avoids the reduction in circuit yield associated with the prior monolithic integration approach and that permits the use of silicon as a substrate for device integration.